The Unition Terminus
If one were to design two cities - a flawless paradise and the bleakest hell - both would find themselves expressed somewhere within the vastness of The Unition Terminus.
Whilst the theoretical existence of alternative and parallel realities has found a degree of acceptance in the mainstream scientific community, it remains an area in which those within more esoteric fields have a decidedly more rich and advanced understanding. The former, for example, has no model that can explain, account for, nor even recognise the existence of limited parallels. These sub-realities, which can be natural - offshoots and splinter realms that never developed into true parallels - or created though the deliberate and controlled fragmentation of time and space, are also known as pocket realities (sometimes dimensions or universes) and exist outside and apart from the more-readily understood cosmological superstructures.
The true parallel realities within this construction are often held to be physically inviolate - with pocket dimensions generally believed to have a fixed connection to a single prime parallel - and phenomena that appear to involve the crossing of such bounds are generally agreed to involve an interaction either between a pocket dimensions and its prime parallel or between multiple pocket dimensions connected to the same prime. Originating as offshoots and splinters (regardless of the causes or catalysts for their creation), such realities function according to the same physical and metaphysical laws, although these can end up being expressed quite differently due to the effects of their fragility and limited size.
Most pocket dimensions, particularly those being intentionally cultivated by human invention, are small enough that they count somewhat - at least for the purposes of thermodynamics - as closed systems. This means, broadly, that they tend towards entropy; an accelerating chaos of decaying and unsustainable energies in which urgent, protean endeavours might have brief windows of potential viability. These are realities born to burn brightly and to be used up, forges for the conception and creation of things - miraculous monsters and monstrous miracles alike - which could never otherwise have existed. Some have theorised that they are the crucibles in which every impossible thing is formed; the origins of all mysteries that fall outside of conventional science.
Larger and more complex pocket dimensions can accommodate a more complete approximation of cohesive physical laws and, as a result, are more stable. Some even host whole, unique ecologies - human and otherwise - and are the stuff and source for many of the myths about lost and extinct civilisations. Perhaps the most famous example is The Unition Terminus: A vast and shifting labyrinth of ramshackle and overlapping architecture, it is both a city and the living idea of cities, a sanctuary and a second-chance with almost as many names as it has residents (The Metropolis Apeirogon, Fractal Paris and Sans Sobriquet being just some of its more persistent and enduring monikers).
Built up over thousands and thousands of years, The Unition Terminus’ culture and customs - even its uneven and unpredictable aesthetics - are a gestalt of the efforts and influences of generations of immigrant residents who were displaced from our prime parallel (and of their descendants). Etruscan archways and Islamic arabesques are paired next to brutalist concretes and grand gothic spires that blot out the sky in between towering glass skyscrapers. To walk through the thronging, polyglottal streets is like being constantly transported throughout time and space, our past and future histories blended and blurred into a heterogenous and anarchic assemblage that still retains a distinctness that is very much all its own.
Unassailably vast, The Unition Terminus is a superposition of all previous, extant and possible cities - as well as the ghost of all the metropolises that could never be built. An exceptional opportunity and endless frustration for those in numerous academic fields (anthropology and urbanology being two that come to mind), the loosest description of the interwoven and interdependent social and economic systems by which the city purports to operate would fill a small and rather impenetrable library. The Unition Terminus is similarly impervious to the codification of mapping or censuses, though many have nonetheless committed their lives to attempting the foolhardy and Sisyphean task of authoring a conclusive work on the city and its peoples.
Even art is insufficient to properly describe The Unition Terminus, though it can come closer than any amount of measurements and mathematics might hope to, and then only in expressions that border somewhere between genius and desperation. Formalism fails because the city is formless, alive and unconstrained. It is a fearsome engine that never stalls and never ceases, fuelled by the sympathetic magic of a citizenry who move through the streets more by instinct than memory. To live in The Unition Terminus is to give part of oneself over to the city: People who end up there either develop a sympathetic simpatico with its rhythms or are driven insane through their insurmountable incompatibilities.
Besides its inestimable sprawl, part of the reason for the continued growth and vibrancy of The Unition Terminus is also the attribute for which it is named. Next to our prime parallel which, by necessity, has a connection (however tenuous or impassable) to each and every pocket dimension that splits off from it, The Unition Terminus has the most prolific known network of similar pathways. While these are still fundamentally transient - their locations within the city and within the pocket dimensions they link to change at frequent but inconsistent intervals - they are uncommonly stable. Safely traversable without any particular preparations, these have led to The Unition Terminus’ expansion into a nexus for intra-parallel exploration.
The pursuit of such discovery drives several aspects of life that set the society in The Unition Terminus apart from its terrestrial alternatives. The evolution of their science, for example, has followed a different path - a result of both the different practical challenges of sustaining a world with no naturally arable land and of developing alongside an undeniable exposure to things that our science either ignores or is ignorant of. There is also an industry of people who seek out and attempt to catalogue the ever-changing array of pathways to other worlds, acting as guides (and sometimes smugglers) to those who have a goal in mind and the means to make the dangers worthwhile.
This is not to say that it is in any way an easy or a trivial enterprise to reach The Unition Terminus, nor that it is any simpler to cross from there to a specific pocket dimension or even back to our prime parallel: There is a reason that enough people have found themselves unwittingly stranded there that a functional civilisation - albeit one very different from those most would recognise - was able to develop. Despite this, The Unition Terminus’ potential access to ever corner of our universe represents an unmatched opportunity for uncovering foundational truths about creation or the chance to create something hitherto unimagined. Even, sometimes, something unimaginable.